Pulse generator system



4, 1951 F. J. GAFFNEY ET AL PULSE QENERATOR SYSTEM Filed Jan. 13, 1944FIG. n

FIG. 2

INVENTORS WILL/AM O. REED 8 FRANC/S J. GAFFNEY Patented Aug. 14, 1951PULSE GENERATOR SYSTEM Francis J. Gaffney, Woburn, and William 0. Reed,

East Walpole, Mass, assignors, by mesne assignments, to the UnitedStates of America as represented by the Secretary of War ApplicationJanuary 13, 1944, Serial No. 518,148

8 Claims. (Cl. 250-36) This invention relates to a pulse generator andmore particular to a circuit for generating pulses having apredetermined duration and time interval between adjacent pulses. Inparticular the invention contemplates a pulse generator used inconnection with a rectangular wave generator to provide a control gatefor setting the pulse generator on or off at times determined'by thecharacteristics of the rectangular waves.

The system hereinafter described may find utility in various fields;Thus it is possible to use such a system in a coding system such asmight be used to distinguish one landing beacon from others in a certainregion. The pulse generator system may also be used, when properlycalibrated, as a means for generating accurately timed pulses tofunction as range markers in a radar system. Other uses will occur tothose skilled in the art.

The pulse generator system in its broadest aspect comprises a blockingtype of oscillator associated with an open delay network so that pulseshaving accurately predetermined frequency and duration are generated,andcontrolled or gated by a control system responsive to rectangularwaves.

Referring now to the drawings, Figure 1 shows a circuit diagram of oneform of pulse generator. figure 2 shows a circuit diagram of amodificaion.

Referring first to Figure 1, the system comprises input terminals I andgrounded. Input terminal I0 is connected through a blocking condenser l2to lead [3 going to control grid M of a vacuum tube I5. Lead l3 hasconnected thereto one terminal of a grid resistor [5 while the otherterminal of said resistor H, the latter being 7 is connected to slidingcontact I! of a potentiometer l8. Across the terminals of potentiometerI8 is connected a bias battery 20 with the polarity as indicated. Thepositive terminal of the bias system is grounded at 2 I.-

Vacuum tube I5 has a cathode 22, of any suitable type, connected by alead 23 to terminal 24 of a variable grid resistor 25. Terminal 24 isalso connected through an isolating resistor 26 to a sliding contact 2!cooperating with potentiometer l8. Vacuum tube i5 has its anode 29connected through a dropping resistor 30 to line 3! leading to thepositive terminal of a high volthave a minimum of three electrodes,thesebeing cathode, control grid, and anode. As shown, however, thevacuum tube 34 is of the pentode type connected up as a tetrode and hascharacteristics suitable for use in this system. Vacuum tube 34 has itsscreen grid 35 and cathode 36 connected on opposite sides of a blockingcon denser 31, the cathode 36 being grounded while the screen grid 35 isconnected through a dropping resistor 38 to lead 3| Suppressor grid 39and anode 48 of vacuum tube 34 are connected toether to function as oneelectrode. This composite anode is connected through a damping resistor42 to one secondary 43 of an iron core type of pulse'transformer 45.Pulse transformers of the type indicated in 45 are well-known in themodulator art and are used in a regenerative oscillator system forcreating sharp pulses. Inasmuch as the characteristics and properties ofsuch transformers are well-known, no further description is deemednecessary. Secondary 43 of the pulse transformer goes on through a lead46 to 3+ lead 3|.

Control grid 33 is connected through a small damping resistance 4'! tothe primary 48 of pulse transformer 45. Primary 48 is connected to oneterminal 49 of a delay line 50 consisting of small inductance elements5| and capacitance elements 52. As is evident, the inductance elements5! are in series while the capacitance elements 52 are connected inparallel across the line in the usual ladder type of delay network. Thelow side of the capacitance elements are grounded at 53. The delay lineis open in the sense that no terminating impedance is provided. Thusreflections may occur.

Pulse transformer 45 has an additional load secondary 55 the lowerterminal of which is connected through a grid resistor 56 to ground.Grid resistor 56 is shunted by a grid condenser 51. The upper terminalof secondary 55 is connected through a damping resistor 58 to thecontrol grid 59 of a vacuum tube 50. This tube is preferably of the sametype as tube 34 and has a cathode 6| grounded at 62 to which isconnected an output terminal 53'. A screen grid 54 is connected to apoint 65 on a grounded resistor 56 whose high terminal 57 is connectedto potentiometer tap 68 operating on resistor 69 connected between B+lead 3| and ground. Between screen grid 54 and cathode 5| is connectedthe customary by-pass condenser l0. Suppressor grid H and anode 12 areconnected together to function as a composite anode. From this compositeanode output terminal 13 is taken. This composite anode is connectedthrough a load resistor 15 to potentiometer tap 68.

It should be understood that the potentials applied to the anodes of thethree vacuum tubes must be carefully controlled for best results. Forthat reason the values of resistors 39 and 38 must be determined. Infact the voltage divider control exercised upon the electrodes of vacuumtube 60 may if desired be applied to tubes and 34. The operation of thissystem will now be discussed and thereafter constants of an operativesystem will be given.

Vacuum tube I5 is normally maintained at cut-off by the application of asufficient negative bias to its grid l4. It is assumed, however, thatthe rectangular voltage waves fed in from a suitable source, such as amulti-vibrator, have sufficient amplitude to raise the grid above itscut-01f value. During the time that grid I4 is above its cut-off value,space current will flow through tube l5. Upon the occurrence of suchspace current the potential of cathode 22 will rise. This rise inpotential is communicated to control grid 33 of the second vacuum tube34 and causes this. control grid to rise above its normal cut-off value,established by potentiometer tap 21. The rise in potential of con trolgrid 33 creates a surge through primary 30 of .the pulse transformer 45to delay line 50. At the same time, space current through tube 34 isestablished by the rise in potential of grid 33 and this results in asurge through winding 43 of the transformer. The two windings 43 and 53are so connected with regard to polarity that one aids the other toefiect regeneration. The net effect is that the potential of grid 33rises far above its cut-off value and a steep voltage pulseis produced.As soon as vacuum tube 34 saturates, transformer action ceases. Thecessation of such action results in a reverse pulse. The delay line 50is designed to cooperate with the rest of the system so that reflectionstherein tend to create sharp pulses having predetermined duration timesand spaced at predetermined time intervals.

The output winding 55 of the pulse transformer may be considered asrepresenting the load and feeding the output tube 60. The actual pulseaction is determined among other things by the potential to whichcathode 22 jumps when grid 14 becomes positive and the time constant ofgrid resistor 25 taken in conjunction With the capacitance of the delaynetwork. Thus by increasing resistor 25 the separation between adjacentpulses may be controlled over a substantial time interval. The pulseWidth itself is controlled by the delay line particularly the value ofthe condensers used therein.

One important consideration which is inherent in all regenerativesystems is the nature of the load imposed upon the regenerative system.In this particular instance the load is not only the winding 55 of thepulse transformer but also tube 60. Thus it becomes important to biastube Bi] and adjust its load resistor tosuch a value that the loads seenfrom windings 48 and 43 of the pulse transformer are suitable. Unlessthis output load is satisfactory, the output of the blocking oscillatoris impaired.

In order to give an example of an operative system, Figure 1 will beredescribed with actual values and types of tubes. Thus vacuum tube maybe a 6J5 with the control grid 14 normally biased to about 35 voltsthrough a 1/ megohm resistor at IS. The potential applied to anode 29was 150 volts. A rectangular wave having an amplitude of '75 volts witha peak duration time of 100 microseconds was applied through a .01microfarad condenser, this being condenser l2. Tubes 34 and 60 were both6AC7. The grid 33 of tube 30 was normally biased to -15 volts, this biasbeing applied through re-- sistor 20 having a value of between 5,000 and10,000 ohms and variable resistor 25 having a value from approximatelyzero ohms to 100,000 ohms. Damping resistance 4'! may be of the order ofabout 100 ohms, while transformer is the customary pulse transformerused in modulators. Plate damping resistor 42 is also low, being about100 ohms and having 250 volts impressed thereon from line 3|. Screengrid 35 was biased to 175 volts. By-pass condenser 31 may have anysuitable value such as .1 microfarad.

Delay line has the inductance elements each of 250 microhenries whilethe condensers 52 are each about 100 micro-microfarads.

Vacuum tube had its control grid 59 biased by resistor 56 of .25 megohmand shunted by condenser 57 of .25 microfarad. The anode T2 of vacuumtube 60 had an adjustable potential of from zero to 250 volts, thisbeing obtained by moving potentiometer contact 68 along resistance 59.Screen grid 54 was biased to about V5 01" the anode potential bychoosing point 68 so that 40,000 ohms above this point remain out of atotal of about 190,000 ohms of resistance 06. Load resistor in theanodecircuit was adjusted to 300 ohms. The damping resistor 50 in the gridcircuit was negligible, being of the order of 100 ohms while by-passcondenser !0 was the usual .1 microfarad condenser.

With the system as above given, a '75 volt rectangular wave could beapplied at any repetition rate up to about 10,000 times per second. Witha signal having the amplitude as indicated, cathode 22 rises 65 voltsabove its normal bias of -l5 volts. When this occurs, control grid 33rises positively from its normal cut-off bias, the rate of rise being afunction of the time constant in the grid circuit. This time constant,as previously indicated, is roughly the product of the eifectiveresistance 25 and capacitance 52 of the delay line. The remainingresistance and inductance in the grid circuit are too small to besignificant. When the voltage of control grid 33 rose to about 5 volts,regeneration occurred and the blocking oscillator functioned to generatepulses. By varying grid resistor 25 over its entire range, pulseseparation of between 3 microseconds to about 100 microseconds may beeffected. The pulse width was approximately 1 microsecond. Therepetition rate of the'rectangular wave for the above value was 2,000cycles per second. The pulse separation may be controlled by controllingthe repetition rate to some extent. In order to decrease the timebetween adjacent pulses, the amplitude of the rectangular wave atcontrol grid l4 must be increased or the delay line made smaller byreducing the number of sections. The pulse width itself may be shortenedby reducing the value of condensers 52. The output from tube 60 is aseries of squared pulses variable in amplitude up to about volts.

Referring now to Figure 2, a bias battery I00 is connected across agrounded potentiometer llll, the negative terminal battery being thehigh side. Sliding contact I02 of the potentiometer is connected to aresistor I03 through junction point I04 and thence to control grid I05of a vacuum tube I06. Across resistor I03 is connected a diode I01, thecathode I08 being connected to the potentiometer end of the resistor,while the anode I09 is connected to the junction point I00. Vacuum tubeI06 has its cathode I I grounded and a screen grid III connected to leadH2 for energizing the anode circuit. Screen grid III and cathode IIOhave the usual by-pass condenser II3 connected across them. Suppressorgrid H5 and anode H6 are connected together to form a composite anode,this latter being connected through a damping resistance I I7 to thesecondary I43 of a pulse transformer I45 similar to pulse transformer 45in Figure 1. The anode circuit continues on through secondary I 33,through a dropping resistor H9 to the anode supply IIZ.

Junction point I04 is connected through a damping resistor I47 toprimary I08 of the pulse transformer and thence on through seriesconnected inductance elements I5! to an input terminal I20. The groundedinput terminal I2I has condenser elements I52 connected across to form aladder type open delay network :50 similar to network 50 in Figure 1.

Pulse transformer I45 has the output winding I22 connected through adamping resistor I23 to the primary I24 of an isolating transformer I25.The secondary I55 of isolating transformer I53 is connected in a mannercorresponding to winding 55 of Figure 1, the corresponding elements inthe system having the same numbers with the addition of a hundredthereto.

The rectangular wave input may be applied directly to the delay line asshown. The diode, which in one instance was a 61-18, is connected acrossa resistance I03 which was fixed at 10,000

ohms. The higher the value of resistance I03, the greater the triggervoltage built up in control grid I05 of tube I06. The control grid I05may be biased below cut-off as in Figure 1, tube I00 corresponding totube 30 in this particular instance.

By separating the load transformer I25 from the pulse transformer I45, agreater degree of control over the value of the load in the pulsegenerating circuit may be secured. Thus by controlling the transformerratio in load transformer I25 as well as by controlling the pulse of thecharacteristic curve upon which output to I60 operates, efiicientoperation of the entire system may be obtained. The control grid ofoutput tube in either of Figures 1 or 2 may be biased at some fixedvalue by suitable battery.

What is claimed is:

1. A pulse generating system comprising: a blocking oscillator, saidblocking oscillator including as a part thereof a vacuum tube havinggrid and anode circuits regeneratively coupled; an open delay line inseries with one of said circuits, for providing accurate spacing for thepulses generated by said blocking oscillator;

biasing means coupled to said blocking oscillator, for causing saidblocking oscillator to be normally cut-ofi; and switching means coupledto said blocking oscillator for impressing on said blocking oscillator aseries of generally rectangular control voltages having an amplitudesufficient to cause said blocking oscillator to become operative, saiddelay line having an electrical length such that the period of saidblocking oscillator is a submultiple of the period of said controlvoltages.

2. The system of claim 1, further including means for varying the biasapplied to said blocking oscillator.

3. The system of claim 1, wherein said delay line is in said gridcircuit and wherein said rectangular control voltages are impressed uponsaid grid circuit to raise the potential of said grid above cut-off.

4. The system of claim 1, wherein said delay line is in said gridcircuit and wherein said rectangular control voltages are impressed onsaid delay line.

5. The system of claim 4, further including a diode for providing adischarge path for said delay line and connected across said gridcircuit.

6. A pulse generating system comprising a vacuum tube having controlgrid and anode circuits; biasing means coupled to said vacuum tube. forcausing said vacuum tube to be normally cut-ofi; means including a pulsetransformer connected in said two circuits, said pulse transformerproviding regenerative coupling so that said vacuum tube and transformerform a blocking oscillator for generating sharp pulses; an open delayline connected in series with said grid circuit; means for impressingrectangular voltage waves on said grid circuit, said waves having asufficiently great amplitude to swing the potential of said grid abovecut-off value and controlling said blocking oscillator, said delay linehaving an electrical length such that the period of said blockingoscillator is a submultiple of the period of said voltage waves; anoutput winding on said pulse transformer and means connected to saidoutput Winding for taking ofi controlled, accurately spaced pulses.

7. The system of claim 6 wherein said output winding circuit includes avacuum tube; and means for biasing said vacuum tube so that said outputcircuit presents a properly matched load for the blocking oscillator.

8. A pulse generating system comprising, a blocking oscillator, saidblocking oscillator including as a part thereof a vacuum tube havinggrid and anode circuits regeneratively coupled, a delay networkconnected in series with one of said circuits to produce a substantiallysquare pulse of accurately controlled duration, means normally biasingsaid vacuum tube to cut-off, and means to disable said last-named meansfor spaced intervals, said delay network having an electrical lengthsuch that the period of said blocking oscillator is a submultiple ofsaid intervals, whereby a plurality of pulses is produced during each ofsaid intervals.

.FRANCIS J. GAFF'NEY.

WILLIAM C. REED.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,110,245 Stocker Mar. 8, 19382,212,173 Wheeler et al Aug. 20, 1940 2,212,420 Harnett Aug. 20, 19402,409,577 Matson, Jr. Oct. 15, 1946 2,436,808 Jacobsen et al. Mar. 2,1948 2,444,782 Lord July 6, 1948 FOREIGN PATENTS Number Country Date578,690 Great Britain July 9, 1946

